1. Field of the Invention
The invention relates to fuel cells with integrated humidification as well as a method for humidifying process gas for the operation of a fuel cell.
Because of their high efficiency and low pollutant and noise emission, fuel cells are very well suited for independent current generation in smaller and medium units, for traction applications, as well as for combined current- and heat generation.
To avoid a desiccation of the electrolyte membrane, it is necessary with fuel cells, especially with fuel cells having proton-conducting electrolyte membranes or polymer electrolyte membranes (PEM cells) that the process gases, i.e., gas containing O2 for the cathode side and fuel gas containing H2 for the anode side, are humidified. Many methods have already been proposed for the humidification of the process gases of fuel cells.
2. Brief Description of the Related Art
EP 0,629,014 B1 describes a method and a device for humidifying process gas for the operation of fuel cells, where water from an external supply line is sprayed into the process gas through a fine atomizing nozzle. The water quantity is adjusted by a dosing valve arranged in the supply line depending on the gas quantity to be humidified and the temperature.
EP 0,301,757 A2 describes a fuel cell with an ion-conducting electrolyte membrane where water is injected into the anode side through an external supply line to humidify and cool the fuel cell.
JP 07,176,313 A describes an arrangement comprised of a fuel cell and a heat exchanger, where water supplied by an external supply line is evaporated by the heat extracted from the used air of the cell and used to humidify the air to be supplied to the cell.
U.S. Pat. No. 6,106,964 describes an arrangement of a PEM-fuel cell and a combined heat- and humidity exchanger comprising a process gas feed chamber and a process waste gas chamber separated by a water-permeable membrane. The water and heat from the process waste gas flow are transferred to the process gas feed flow through the water-permeable membrane. Although product water is used directly in this arrangement for humidifying the fuel cell, it is difficult or impossible to regulate the feedback portion of the product water. Furthermore, any contaminations in the product water, such as metal ions, are continually circulated, which can lead to an impairment of the cell and the water-permeable membrane during extended operation.